1. Field of the Invention
The present invention relates to an input stage for a low-noise high-frequency broadband amplifier having an amplifier element.
2. Description of the Prior Art
In processing small signals, special attention must be paid to noise in the circuitry. Noise sources include, for example, ohmic resistors, electron tubes and transistors. As noise power increases with increasing bandwidths, it is often advantageous to use narrow-band amplifiers to amplify small signals. When a number of signals of varying frequency are provided at the input stage of the amplifier, a number of narrow-band pre-amplifiers must be arranged at the input stage, dependent on the bandwidths and center frequencies of the signals. The pre-amplifiers must be capable of switching, by means of coaxial switches, to attain the desired frequency.
Further, in processing high-frequency signals, the individual stages must be matched to the characteristic impedance in order to avoid reflective losses.